Imaging

The minimum radiographic workup necessary for evaluation of an acute dislocation or suspected subluxation is a true anteroposterior (AP) view and an axillary lateral view. These images will allow accurate determination of the position of the humeral head relative to the glenoid.

A true AP radiograph is obtained by angling the x-ray beam 45 degree relative to the sagittal plane of the body. A scapular Y or transcapular view can also give information about the position of the humeral head, but it is not as accurate as an axillary view. If a standard axillary view cannot be obtained, a Velpeau axillary view without removing the patient’s arm from the sling will suffice.

In the office setting, a true AP view of the shoulder with the arm in internal rotation may demonstrate a Hill-Sachs lesion. A Stryker notch view is a special view that will also demonstrate a Hill-Sachs lesion.

West Point axillary view may prove helpful in a patient suspected of having had an episode of instability. Take the image with the patient prone so the anterior glenoid is shown in profile without an overlying acromial shadow. This view demonstrates the glenoid rim better.

Adjuvant imaging techniques add vital information about the three-dimensional relationship and architecture of the joint or confirmation of the presence of a Bankart lesion, either bony or soft-tissue. Computed tomography (CT) demonstrates bony injuries or abnormalities including glenoid dysplasia, congenital version anomalies, acquired version abnormalities from erosion, and glenoid rim fractures.

In addition, it allows measurement of the size of a humeral head defect (Hill-Sachs lesion) in cases of chronic instability. When combined with intra-articular dye, CT arthrography also demonstrates Bankart lesions and articular erosions.

Magnetic resonance imaging (MRI) with or without gadolinium has enormous popularity, although unfortunately it is often used as a screening tool in the evaluation of patients. Its role should instead be to confirm the presence of lesions that may need surgical treatment. MRI or CT with contrast are valuable for identifying labral tears, capsular injuries, or bony deficiencies.

Although the arthroscope can be used for diagnostic purposes, we prefer to identify coexisting pathology (rotator cuff tears), the degree of capsular laxity, and the extent of labral pathology with the appropriate imaging studies preoperatively, so that the appropriate surgical procedure can be selected and planned.

In some cases, however, where the quality of capsular tissue is questionable by imaging studies or concomitant pathology is highly suspected but not found preoperatively, a diagnostic arthroscopy performed at the start of a planned open procedure can help add additional information, and possible arthroscopic treatment) regarding intra-articular pathology.

A prolonged arthroscopic evaluation and/or treatment done immediately prior to performing an open procedure can distort tissue planes, and in some cases add no new information but only create technical problems for the planned open procedure.

Recent studies show MRI arthrography to be highly sensitive and specific for detecting capsulolabral lesions. CT is preferred if osseous pathology is suspected. CT is particularly helpful in the evaluation of glenoid retroversion in patients with posterior instability. CT arthrography can also be used to show chondral erosion, labral detachment, or excessive capsular redundancy.